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From: Oleg Tsvinev <oleg.tsvinev@gmail.com>
Date: Mon, 15 Aug 2011 13:39:23 -0700
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Subject: Cassandra in Multiple Datacenters Active - Standby configuration
To: Cassandra Users <user@cassandra.apache.org>, hector-users@googlegroups.com
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Hi all,

I have a question that documentation=C2=A0has not clear answer for. I have
the following requirements:

1. Synchronously store data in datacenter DC1 on 2+ nodes
2. Asynchronously replicate the same data to DC2 and store it on 2+
nodes to act as a hot standby

Now, I have configured keyspaces with o.a.c.l.NetworkTopologyStrategy
with strategy_options=3D[{DC1:2, DC2:2}] and use LOCAL_QUORUM
consistency level, following documentation here:
http://www.datastax.com/docs/0.8/operations/datacenter

Now, how do I assign initial tokens? If I have, say 6 nodes total, 3
in DC1 and 3 in DC2, and create a ring as if all 6 nodes share the
total 2^128 space equally.
Now say node N1:DC2 has key K and is in remote datacenter (for an app
in DC1). Wouldn't Cassandra always forward K to the DC2 node N1 thus
turning asynchronous writes into synchronous ones? Performance impact
will be huge as the latency between DC1 and DC2 is significant.

I hope there's an answer and I'm just missing something. My case falls
under Disaster Recovery in
http://www.datastax.com/docs/0.8/operations/datacenter but I don't see
how Cassandra will support my use case.

I appreciate any help on this.

Thank you,
  Oleg